The invention relates to hetero-composite, preferably self-bulking, textile yarn with high stretch recovery, produced from a high-shrinkage, latent stretch, melt spun biconstituent fiber and one or more lower shrinkage fibers.
Yarns which exhibit good bulk and stretch and recovery are made by a variety of processes, including false twist texturing of non-elastic or hard yarns, bicomponent yarns, wrap covering a hard yarn onto an elastomeric yarn, air covering or entangling a hard yarn with an elastomeric yarn, and core spinning of staple yarn covers on an elastomeric yarn. See, for example, U.S. Pat. No. 4,861,660 to Ishii. Fabrics of enhanced bulk, stretch and recovery properties are made by incorporating one or more of these yarn types into the fabric and/or by using an elastomeric, such as spandex, yarn, which is fed separately into the fabric production process.
Fabrics with good stretch and recovery properties generally require separate processes to prepare the hard yarns or at least a separate yarn feed for incorporating a stretchable, elastomeric yarn. Often the stretchable yarns will require special tensioning devices. For example, the elastomer often requires a covering step which can be expensive, slow, and requires careful control of elastic tension or draft. Once covered, e.g., by wrapping or air entangling, the yarn is still elastomeric in nature. Variability in tensioning of the elastomer component can lead to quality defects. Also, if the elastomer is not pre-covered other problems may occur, such as dye uniformity problems because elastomers dye differently than companion yarns, and/or early failure of bare elastomer which has lower tenacity than the companion yarns.
Ishii describes asymmetric biconstituent filament yarns that can be knitted and woven with nylon yarns in Examples 15 and 16 respectively. These examples teach knitting and weaving the biconstituent filament yarn and the nylon yarn separately in a fabric. In light of the extremely high shrinkage of biconstituent filament yarns, which are high stretch yarns, Ishii recognizes that relaxation of the biconstituent filament yarns is necessary to handle the yarn prior to making the fabric.
High stretch yarns require careful control of yarn tension to achieve uniform properties, and these properties can fluctuate due to denier variations, finish level, etc. Therefore, Ishii prefers tensioning the yarn to insure a uniform feed in length and elastic properties in the fabric structure. However, tensioning also requires capital investment and maintenance.
Moreover, it is often desirable to use yarns which have not been relaxed during spinning at all. This retains the maximum shrinkage, both recoverable and non-recoverable, in the biconstituent filaments, providing for optimum stretch and bulking potential in the composite yarn.
Thus, there is a continuing need to provide yarns and articles therefrom, that exhibit desired stretch and recovery properties, and in particular, yarns which have not been fully relaxed prior to making fabrics and articles therefrom. It is also desirable to design a process for making yarns with desired stretch and recovery properties which does not require tensioning.
While 100% biconstituent yarn can be useful, the economics and the stretch recovery properties of the biconstituents will often show best in composite yarns and fabrics. In many fabrics a content of 10-50% is adequate to provide useful stretch recovery properties, and other tactile and aesthetic benefits. The yarn of the present invention fulfills the continuing need to provide yarns and articles therefrom that exhibit desired stretch and recovery properties, and also overcomes the problems associated with relaxed, high stretch biconstituent filament yarns of the prior art. The present invention achieves this by providing a hetero-yarn where the biconstituent filament yarns are pre-combined with a companion yarn in a unitary yarn structure. Such hetero-yarn does not require relaxation in order to handle the yarn prior to making a fabric. Rather, the xe2x80x9celastic potentialxe2x80x9d of the hetero yarns of the present invention is integrated at the biconstituent processing stage. These hetero-yarns can be treated as hard yarns in fabric manufacture. The elastic potential is activated in the finishing of the fabric. In addition, s/z twist control is not required.
The hetero yarn of the present invention overcomes many of the drawbacks of Ishii in particular. For instance, the hetero-yarn of the present invention avoids heat cross-linking or heat relaxing the yarn prior to use. This is an advantage over Ishii, which preferred a two-step thermal cross-linking process. The hetero yarn of the present invention also avoids the need for tensioning, as preferred in Ishii, by feeding the biconstituent yarn in the hard yarn state. As noted above, tensioning requires capital investment and maintenance. Feeding the biconstituent in the hard yarn state is therefore more economical and reliable than the process described in Ishii, providing yarn properties are consistent.
In many cases high shrinkage can be accommodated in fabrication or used to an advantage, and the present invention makes use of this. Applicants have found that greige fabric and garment constructions from the yarn of the present invention can be adjusted to allow for the extra shrinkage. Further, high shrinkage can be used to an advantage in many fabric constructions, for instance to increase fabric bulk in hetero yarn structures, or to reduce or control knit fabric porosity in bottomweight knits. Also, yarns slightly relaxed on the face plate during spinning (5%-20%) substantially reduce non-recoverable shrinkage in finishing and enhance yarn toughness for knitting, while substantially retaining hard yarn package delivery characteristics.
Moreover, the co-mingling and co-texturing of yarns is more productive where two yarns to be co-mingled and co-textured have similar properties. In the present invention, the biconstituent yarn in the drawn pre-relaxed state has properties similar to the hard companion yarns, and very different from standard elastomeric fibers. Thus, the biconstituent yarn of the present invention can be air textured or air mingled efficiently with other hard companion yarns.
With the present invention, premature shrinkage can be controlled by proper package formation and package hardness. Applicants have found that it is possible to wind large packages of monofilament biconstituent in the unactivated state, and to store them for several months without significant loss of properties or change in package hardness.
In addition, the high shrinkage associated with biconstituent filaments requires that, on shrinking, the lower shrink companion yarn must bulk. The present invention envisions that either straight or textured companion yarns may be combined with biconstituent yarns. Straight companion yarns will tend to form loops which can be advantageous in some fabrics (say formation a terry surface fabric) or a negative in other cases (may increase fabric picking). However, companion yarns which have been cubicly crimped, or textured, have natural bends for storage of the added bulk when the biconstituent filaments shrink; biconstituent yarns with textured companion yarns have smoother or cotton-like surfaces which are often advantageous in many apparel applications.
The above-mentioned advantages are obtained by the present invention, which provides a hetero-composite yarn comprising a combined biconstituent yarn and a companion yarn, wherein the biconstituent yarn comprises at least one biconstituent filament including an axial core comprising a thermoplastic, elastomeric polymer and a plurality of wings attached to the core and comprising a thermoplastic, non-elastomeric polymer.
The above-mentioned advantages are also obtained by the present invention which provides a process for making a hetero-composite yarn, comprising spinning a biconstituent yarn and a companion yarn together, wherein the biconstituent yarn comprises at least one biconstituent filament including an axial core comprising a thermoplastic, elastomeric polymer and a plurality of wings attached to the core and comprising a thermoplastic, non-elastomeric polymer.